1. Field of the Invention
The present invention relates to a fuel filling device that fills hydrogen or compressed natural gas as fuel into a vehicle, and to a method of detecting fuel leakage of a fuel filling device.
2. Description of Related Art
Development is proceeding on hydrogen automobiles and compressed natural gas automobiles using hydrogen gas and compressed natural gas for fuel as next-generation automobiles. These automobiles are characterized by low emission levels of carbon dioxide gas, NOx, SOx, and other pollutants.
When refueling these automobiles, the automobiles are driven to a refueling station provided with a fuel filling device (dispenser) that fills the hydrogen gas or compressed natural gas used as fuel, and fuel is then replenished at that refueling station in the same manner as current gasoline-fueled automobiles.
Studies are being conducted on the safety and other aspects of these automobiles and fuel filling devices (refer to, for example, Japan Gas Association, “Safety and Technical Guidelines for Compressed Natural Gas Stations”, April 1998, p. 44).
In the case of using compressed natural gas as fuel, underground supply pipes that supply compressed natural gas to homes and corporations are used in fuel filling devices. Compressed natural gas that has been supplied through a pipe that branches from a supply pipe used to feed compressed natural gas to homes and corporations is boosted in pressure with a compressor, and this compressed natural gas is then supplied to a plurality of storage tanks at respectively different filling pressures followed by maintenance and management of that supply.
In the case of filling compressed natural gas into the fuel tank of an automobile, compressed natural gas is begun to be supplied by removing compressed natural gas from one of the plurality of storage tanks at a low filling pressure, and then the pressure of the automobile fuel tank approaches the pressure of the storage tank, the supply path switches to another storage tank having a higher filling pressure than this storage tank.
In this manner, by supplying compressed natural gas from a tank while sequentially switching to a storage tank filled at a higher filling pressure, filling is carried out so as not to cause rapid filling accompanying sudden changes in pressure.
The maximum filling pressure of storage tanks in conventional compressed natural gas fuel filling equipment is about 25 MPa.
In the case of using hydrogen gas for fuel, a method in which hydrogen gas is generated by primarily reacting natural gas and water at a high temperature of 700-800° C., and a method in which hydrogen gas is generated by electrolysis of water, are being considered.
The hydrogen gas generated with these methods is boosted in pressure by a diaphragm-type pressure booster, and then filled into a plurality of storage tanks at respectively different pressures followed by maintenance and management of that supply.
During filling of fuel, similar to the case of compressed natural gas, filling is carried out by removing fuel while sequentially switching the plurality of fuel tanks among low pressure, intermediate pressure and high pressure tanks so as to prevent the occurrence of rapid filling.
The maximum pressure of hydrogen gas fuel storage tanks in current prototype equipment is about 40 MPa.
FIG. 5 shows an example of a fuel filling device that fills hydrogen gas or compressed natural gas into the fuel tank of an automobile.
This fuel filling device 50 is provided with a fuel supply adjusting section 51 that adjusts the amount of fuel supplied, a filling hose 61 coupled thereto that feeds fuel to a fuel tank T of an automobile W, a nozzle 65 arranged on the end section of the filling hose 61 that supplies fuel by being removably coupled to a line 73 running to fuel tank T of automobile W, and a discharge hose 70, one end of which is coupled to nozzle 65, while the other end is open to the atmosphere via a valve 69 after passing through fuel supply adjusting section 51.
A fuel distribution line 52 that sends fuel from a fuel source 60 to filling hose 61 is provided in fuel supply adjusting section 51.
A mass flow meter 53, a flow rate adjusting valve 54, a cutoff valve 55, and a pressure switch 56 are provided in fuel distribution line 52.
Fuel source 60 is composed of a plurality of storage tanks 60k, 60m, and 60n into which fuel has been filled at mutually different pressures, namely a low pressure, an intermediate pressure and a high pressure, and these storage tanks 60k, 60m, and 60n are switchably connected to fuel distribution line 52.
Nozzle 65 is a three-way valve, filling hose 61 is connected to connection port 65a of connection ports 65a through 65c, and discharge hose 70 is connected to connection port 65b. The remaining connection port 65c is located at a filling port 66, and filling port 66 is able to be removably connected to a receptacle 71 serving as the connection port of fuel tank T of automobile W in a single operation by means of a pipe coupling structure.
To prevent the fuel filling device from being damaged or the fuel from leaking when filling hose 61 and discharge hose 70 are subjected to a predetermined tensile force or greater due to automobile W mistakenly being driven away in the state in which filling hose 61 and discharge hose 70 are still connected, or due to being subjected to an external impact, an emergency release pipe coupling 62 is provided at an intermediate location of filling hose 61 and discharge hose 70 that is provided with a cutoff function, which together with releasing when acted on by a prescribed tensile force, prevents outside air from entering the hose.
In fuel filling device 50, filling operation is performed with the series of operations described below.
In the standby state, the connection port 65a with filling hose 61 of nozzle 65 of fuel filling device 50 is closed, and connection port 65c on the side of automobile W and connection port 65b on the side of discharge hose 70 are connected.
When filling automobile W with fuel, nozzle 65 is connected so that its filling port 66 engages with receptacle 71 of automobile W.
Next, after a handle 65d of nozzle 65 is operated so as to connect filling hose 61 and receptacle 71 of automobile W by connecting connection port 65a and connection port 65c, fuel is filled from fuel source 60 into fuel tank T of automobile W by pressing a filling start button (not shown) arranged on fuel supply adjusting section 51 of fuel filling device 50.
Fuel is then filled into fuel tank T of automobile W through filling hose 61, nozzle connection ports 65a and 65c, and receptacle 71 from fuel supply adjusting section 51.
During filling, the storage tank among storage tanks 60k, 60m and 60n having a filling pressure which is higher than the pressure of fuel tank T of automobile W at the start of filling while also being the closest to the pressure of fuel tank T. At the same time, cutoff valve 55 is opened and discharge valve 69 is closed.
Together with then suitably adjusting the opening of flow rate adjusting valve 54 by controlling the drive air supplied to flow rate adjusting valve 54 by a control section 68 based on the pressure difference between the pressure of fuel distribution line 52 detected by pressure switch 56 and the storage tank pressure detected by pressure switch 67, filling is carried out by sequentially increasing the filling pressure in a stepwise manner so as to switch to the storage tank having next highest filling supply pressure when the pressure difference between the pressure of filling hose 61 and the pressure of the storage tank becomes smaller.
When the fuel is filled to a prescribed pressure value, and the value detected by pressure switch 56 reaches a prescribed pressure, pressure switch 56 emits a signal via control section 68 that causes a lamp and so forth to light (not shown) to inform that filling is completed, while at the same time, cutoff valve 55 closes and discharge valve 69 opens.
When filling is completed, the connection ports of nozzle 65 are switched by handle 65d. Namely, connection port 65c and connection port 65b are made to be connected.
In this manner, when the connections ports of nozzle 65 are switched by operating handle 65d so that nozzle connection port 65c on the side of receptacle 71 and connection port 65b leading to discharge hose 70 are made to be connected, fuel retained in line 73 running between nozzle 65 and cutoff valve 74 of fuel tank T of automobile W is discharged into the atmosphere via discharge hose 70.
Next, fuel filling operation is completed by disconnecting nozzle 65 from receptacle 71.
Since nozzle 65 is a three-way valve, the direction in which the connection ports are connected can be confirmed from the direction of handle 65d. 
FIG. 6 shows the changes in pressure of filling hose 61 and discharge hose 70 during the filling operation process of this fuel filling device 50.
During standby, the pressure of filling hose 61 maintains a pressure equivalent to filling pressure PF of fuel tank T, and at the start of filling, rapidly drops to the pressure of the coupled storage tank, increases to a desired pressure by sequentially switching to a storage tank of the next highest pressure, and then reaches a standby state at a final filling pressure PF at completion of filling.
On the other hand, although the pressure inside discharge hose 70 increases in order to discharge high-pressure fuel remaining at completion of filling to the atmosphere at the start of the standby period, it is nearly at atmospheric pressure during the other steps.
In the case of a conventional fuel filling device 50, fuel from the previous refueling is retained in filling holes 61 when in a standby state in which fuel is not being filled into automobile W.
Hydrogen is a gas that has the potential to explode in the presence of an ignition source at a concentration of 4.0-75.0% in air. In addition, methane, which is the main component of compressed natural gas, is a gas that has the potential to explode in the presence of an ignition source at a concentration of 5.3-14.0% in air.
Consequently, it is not desirable to allow these gases to be retained within hoses and other lines.
At the current filling pressure at which fuel is filled into an automobile fuel tank T, the distance capable of being traveled by the automobile on a single refueling is about 200 km.
Although this traveling distance is determined by the capacity of the fuel tank T installed on the automobile W and its filling pressure, since there are limitations on the degree to which the capacity of fuel tank T installed on automobile W can be increased, in order to extend the traveling distance beyond 200 km, it is necessary to increase the pressure at which fuel is filled into fuel tank T, and higher filling pressures are desired such as increasing filling pressure from the current level of 40 MPa to 100 MPa.
However, in the case of filling device 50 of the prior art, when the filling pressure is increased, residual fuel remains at a high pressure within filling hose 61 or other lines during the standby state.
If fuel is allowed to be retained in the lines at this high pressure, fuel may permeate into the packings used in component machinery due to penetration, and this permeated fuel may cause deterioration of the packings as a result of swelling inside the packings when pressure drops at the start of filling.
Since hydrogen gas in particularly is highly penetrable with respect to the packings due to its small molecules, allowing hydrogen to be retained in the lines was undesirable.
In addition, in the case fuel is allowed to be retained in the lines in a high pressure state, since the inside of nozzle 65 reaches a high pressure, the pressing force of the packing against the surface inside nozzle 65 that contacts the packing becomes higher, resulting in the problem of it being difficult to open and close the valve of nozzle 65, while also making it difficult to attach and release nozzle 65 to and from automobile W.
In view of the above problems, an object of the present invention is to provide a fuel filling device capable of preventing deterioration of packings of the device in the case of filling fuel at a high pressure, and capable of facilitating operation of a filling nozzle.